This application claims priority of European Patent Application No. 99308221.3, which was filed Oct. 18, 1999.
1. Field of the Invention
This invention relates to digital communications apparatus.
2. Description of the Related Art
A desirable feature in digital communication apparatus is the ability to record speech. In, for example, a digital mobile phone, this ability would enable the phone to act as a telephone answering machine, or to record a voice memo, or to record a conversation taking place over the telephone. An important consideration, particularly in a digital mobile phone, is the amount of memory that has to be provided for this purpose. Previous attempts at providing speech recording in a digital mobile phone have not made efficient use of memory space, and thus required either an unacceptably large memory, or utilised a smaller memory which was insufficient for some purposes.
According to one aspect of this invention there is provided digital communications apparatus including a comfort noise estimator for providing silence frames containing information representative of background acoustic noise, a comfort noise generator for providing comfort noise for simulating background acoustic noise, and speech record/playback means adapted, on record, to store speech frames substantially only during the presence of speech, to store one or more silence frames at the end of the presence of speech, and to store data representative of the duration of the absence of speech, and adapted, on playback, to provide as output speech signals derived from the stored speech frames and, in dependence upon the stored one or more silence frames, comfort noise from the comfort noise generator for a duration represented by the stored data.
The apparatus may be a digital mobile phone including a transmitter adapted to be switched on only for transmission of frames containing useful information, and wherein the comfort noise generator is adapted to provide comfort noise in dependence upon silence frames when no speech frames are received.
The apparatus may include a speech encoder for encoding speech into speech frames and for providing input to the comfort noise estimator for providing said silence frames, whereby said speech frames stored by the speech record/playback means are those encoded by said speech encoder, and a speech decoder for decoding stored speech frames and for providing in the output of the speech decoder comfort noise generated by said comfort noise generator in dependence upon stored silence frames.
The digital mobile phone may be a Global System for Mobile Communications (GSM) phone.
Said stored data may comprise a count of speech frames occurring during the absence of speech.
Said stored data may comprise a respective dummy frame of minimal length for each speech frame occurring during the absence of speech.
According to another aspect of this invention there is provided a method of recording/playing back speech in digital communications apparatus, the method including, for recording, storing speech frames substantially only during the presence of speech, storing one or more silence frames, containing information representative of background acoustic noise, at the end of the presence of speech, and storing data representative of the duration of the absence of speech, and, for playback, providing as output speech signals derived from the stored speech frames and, in dependence upon the stored silence frame or frames, comfort noise for simulating background acoustic noise for a duration represented by the stored data.
Said stored data may comprise a count of speech frames occurring during the absence of speech.
Said stored data may comprise a respective dummy frame of minimal length for each speech frame occurring during the absence of speech.